Ask Surly Amy and Elizabeth: Cats, Genetics and Diseases

Message: Hi guys. I need your help to clarify a question that’s been bugging me for a while now. I’m a crazy cat lady and so is a friend of mine. We meet over coffee to discuss our “babies.” She said her cat – a beautiful Norwegian with probably the lushest coat I ever saw on a cat – was falling ill (urinary tract problems mainly) because it was not a pure breed but had some Maine Coon blood. Now, if I understand things correctly, that should not be the case – introducing new genes in a gene pool, diversifies it and leads to healthier specimens because it makes genetic abnormalities less likely to occur. I have two ferals at home who NEVER fall ill, eat trash (not that I feed them trash, but they find their way to raid trash cans), drink toilet water and nothing touches them. The Norsk skogkatt is a natural breed, so I thought that like the feral it would have a higher chance of a wide gene pool or at least would be healthier than the man-made, inbred breeds.

This question wasn’t originally sent in as an, Ask Surly Amy. It was just a was a general question sent in by a reader to our contact form, but I snagged it! Because I knew I had the perfect person to help answer it!

That perfect person is one of the contributors over on Mad Art Lab, the super-smart and talented, Elizabeth Finn. Elizabeth is not only a creative-contributor to Mad Art Lab, she is also a Doctoral Candidate in genetics at Stanford University. She is our go-to gal for all our super-geeky genetics questions over at the lab and she was more than happy to give us a quick, yet detailed response, as to why mixed breeds aren’t always free from diseases.

From Elizabeth:

Hybrid vigour is a real thing, and probably what the letter-writer is referring to. If you take two very inbred animals, and cross them, the resulting animals will generally be healthier than either parent. And this is for essentially the reason she describes: most genetic disorders are recessive, and so more heterozygosity in a genome, which is created by crossing two different inbred lines, means fewer genetic disorders. But there are some caveats here, particularly:

As you start breeding back onto either of the parental inbred lines, all of the disorders come back. Assuming there /is/ a disorder, and that the hybrid escapes it by being heterozygous, then crossing back to a parental line will uncover that disorder 1/2 of the time by the first generation, 3/4 of the time by the second generation, and 7/8 of the time by the third generation. Genetic diversity via hybridization disappears very shortly after that hybridization disappears. So knowing a cat is “part” Maine Coon doesn’t really help.

This also assumes that the disorder is (1) genetic and (2) recessive. I am not a veterinarian, but WebMD suggests many issues that could cause these issues other than congenital problems. So it very well might not be genetic. And while many genetic disorders are recessive, the most common genetic disorder in cats (feline hypertrophic cardiomyopathy) is dominant, and as such wouldn’t be subject to changes based on hybrid vigor or heterozygosity.

Hope that helps!

Thanks Elizabeth!

And to our reader, urinary tract infections often have dietary causes and nothing to do with genetics so that may be something for your friend to bring up when next speaking with her vet.

Now, go snuggle those kitties while you can and happy holidays from all of us at Mad Art Lab and at Skepchick!

Awwwww, who’s a cute lil fuzz ball! :)

~Amy

Got a question you would like some Surly-Skepchick advice on? Send it in! We won’t publish your real name, unless you want us to and creative pseudonyms get bonus points! Just use the contact link on the top left of the page.

Amy Davis Roth (aka Surly Amy) is a multimedia, science-loving artist who resides in Los Angeles, California. She makes Surly-Ramics and is currently in love with pottery. Daily maker of art and leader of Mad Art Lab. Support her on Patreon. Tip Jar is here.

9 Comments

Hey great post, as someone who has worked as a vet nursing assistant and now in vet school I can say with a little confidence that cats get UTIs all the time, in all breeds. Without knowing the specific problem her cat suffers from it is hard to tell if it is genetic or not. Also, UTIs in cats can have different aetiologies depending on the sex of the animal, whether it has been neutered, the diet the animal eats, stress levels, etc etc. And as in humans, some animals are just ‘prone’ to these problems, which does have a genetic basis but probably not in the way the writer is thinking!

I hope for your cat’s sake you never ever cllean your toilet bowl as the chemicals could eventually ruin your cat’s hepatic system. Also, gross. Tons of bacteria. I’d say you have a nice healthy mixed breed. Make sure you put out enough fresh water so they don’t feel the need to drink from the toilet, and keep the bathroom door closed.

@Luna: We had to switch from a plastic seat to a heavy wooden one a while back because the cats would try to open the lid. Again, as with the trash – it’s not that we let or encourage them to drink from the toilet but they do try and husband does sometimes forget to put the lid back down. They have a perfectly good and functioning water fountain (that simulates running water) and a few water bowls, but as all cats – they prefer anything they caught “hunting”, be it food or water.
I don’t use regular household chemicals because they’re too harsh – a very mild detergent, vinegar, baking soda and elbow grease are enough.

Ugh, the ‘hybrid vigor’ thing drives me nuts! Yes, consistently breeding selectively in favour of any one trait while ignoring all others can (dare I say, “will”?) result, over time, in the increased prevalence of heritable disorders/diseases in a population.

But ignoring the semantic issues around the use of the word ‘hybrid’ (don’t get me started…), with a few notable exceptions (e.g. various blood-cell-related genes in areas where malaria is prevalent and medical care is not) it is not true that heterozygous individuals will be healthier or more ‘fit’ than homozygous individuals.

The oft-repeated “wild populations are healthier!” claim is terribly misleading in general. Anyone who’s spent much time studying wild populations can tell you that no, there’s nothing making (the vast majority of) them especially ‘healthy’ compared to (the vast majority of) their selectively-bred counterparts.

Heritable disorders absolutely do show up, although individuals showing severe defects (‘showing’ as in ‘part of their phenotype’) tend to have low survival rates (not to mention reproductive success rates…) without human intervention, so a given population may appear to be healthier. Among individuals who manage to survive long enough to be observed by researchers there are plenty of diseases, disorders, and parasites to go around (assuming you bother to look closely enough… individuals can certainly appear to be healthy when glanced from a distance).

Don’t forget that there are plenty of ‘wild’ populations that are heavily inbred, too! (e.g. “founder effect”) Although a very high level of inbreeding is often observed to be negatively related to population-level fitness in the face of a changing environment, the level of inbreeding does not automatically determine the (relative) fitness of a given individual or a population. Why would it?

I would argue instead that most of the heritable defects/disorders in selectively-bred animals are the direct result of humans intentionally selecting in favour of a trait that would be otherwise detrimental. There are reasons why wild animals don’t all look like baby primates or adult swans! The actual traits people have chosen to select for (followed closely by “the traits people didn’t know to look for or have chosen to ignore”) are far more relevant to the health of any ‘breed’ than its genetic homogeneity per se.

I agree, “hybrid vigor” is widely misunderstood. The “vigor” is usually only related to phenotype size (bigger), not necessarily to phenotype health. Since many plants are grown for food, farmers want big phenotypes, so they plant hybrids. Essentially all maize planted in the US is hybrid. Bigger is not (usually) more healthy. Many hybrids are infertile (mules for example) because of genetic incompatibilities.

I am not a cat person (I am allergic), but it is my understanding that many cats develop kidney problems, and if your cats are drinking out of the toilet, you are not giving them enough water. Giving them more water is better than putting the toilet lid down. There probably isn’t much risk of a cat catching a human disease from drinking out of its owner’s toilet. Licking its paws after traipsing around the apartment probably exposes it to every disease the owner has ever had, and then some.

Chemicals around the home are likely a greater problem, including things like persistent organic pollutants from things like fire retardants in furniture that collect on dust. Kidneys are high metabolic rate organs, so they are one of the first to go when there are problems with mitochondria biogenesis (heart, liver and brain are too).

First of all, Amy, thank you for answering my question. You clarified a lot for me.
As for UTI in cats – and I heard this from my vet – yes, the causes are primarily dietary but some breeds or cats are more susceptible to these infections, and genes do play a part. She also said that gingers have overall “weaker” immune systems.
I knew already that joint and heart problems in cats often have genetic causes.
My two ferals do not just appear healthy, they are healthy. Over the six years, I’ve had them, one of them had a cold once – meaning it sneezed for two days, and that was it. We regularly go for check-ups and all they ever need is de-worming/hairball removal.
Also thanks to all who contributed to answering my question :)